Very nice! I/O working stable so far, after a small firmware adjustment.
After having the physical prototype in front of me, I was able to figure out a better layout which leaves the unused header pins accessible so the board can be placed on top of the Core
Next will be experiments chaining two of these shields for 6in/6out!
Current prototype seems to invert the phase on its outputs, the codec seems to handle differential/pseudo-differential differently (huh?) so I’ll factor this in for the next revision.
Noticing some interference with the audio jacks I am using for abuse-testing. Inserting a cable can cause nasty electromagnetic spikes from SGND reflecting onto the I2S data lines which can throw off the shield’s codec sync. Not good enough! The Axoloti/Ksoloti Core has been immune to such spikes (even with the shield connected).
Upgrading to a 4-layer board instead of 2 seems like a good idea, and while we’re here, we tuck in the I2S lines on an inner layer (stripline!). The design must simply be more robust, especially for haphazard DIY wiring situations. As always, if anyone has some suggestions or insights feel free to share.
(I’ve never been very clear on the SGND circuits in the Axoloti (and now Ksoloti) schematics - I was under the impression that the 33 ohm resistors and schottky diodes are meant to protect the codec/amp pins from the above surges - but it seems this resistance/potential discrepancy between SGND and GND causes the above problems on the I2S lines?)
